1. Field of the Invention
This invention relates to a composite material, and more particularly to a metal-based composite material and a method of producing the same by impregnating a matrix metal consisting of Al or an Al alloy containing Mg, Cu, Si or the like into a porous preform containing a metal hydride.
2. Description of Related Art
As a method of providing a dispersion-reinforced or fiber-reinforced type metal-based composite material by impregnating a metal melt as a matrix into a porous preform made of a reinforcing material, there are known techniques such as molten metal penetration method, melt casting method and the like disclosed in JP-A-61-295344, JP-A-8-117964 and the like.
In the conventional technique of producing the composite material by impregnating the metal melt into the porous body, however, the outermost surface layer is covered with a chemically stable reaction product layer such as an oxide or the like, or the oxide and the like are at a chemically or physically adsorbed state as an impurity, so that the wettability of the metal melt to a shaped body is poor and hence it is difficult to form a composite only by contacting them with each other. This means that an active energy inherent to free surface of the metal can not effectively be utilized for forming the composite material in the conventional technique.
On the other hand, a method of forming the composite material by surely impregnating a metal melt into a porous body is examined. In this case, it is required to apply a very high pressure, or it is required to preliminarily heat the preform at a high temperature in an inert gas, or it is required to add a specific element or compound for improving the wettability to the melt or prefrom (for example, JP-A-61-165265, JP-A-62-67133 and the like). Of course, it is required to use a special equipment for conducting the application of pressure or the preheating.
As the other conventional technique, there are proposed methods wherein pressure is not applied to the metal melt, or the preform is not preliminarily heated and the like (for example, JP-A-1-279713, JP-A-1-279729, JP-A-1-279721 and the like).
Such a conventional technique not using the pressure application of the preheating is a method wherein a given amount of a metal fluoride is added to the preform and the wettability is improved by utilizing a reducing action of fluorine to the impurity to promote the composite formation. Even in this method, the active energy inherent to the free surface of the metal is not effectively utilized for forming the composite material. Furthermore, fluorine included in the metal fluoride is a gas at room temperature and indicates a highest electronegativity among all elements and is a most reactivity rich substance and hence reacts with any elements other than helium, neodymium and argon. Therefore, it is unfavorable to frequently use such a metal fluoride or the like in industrial applications from a viewpoint of an environment.
It is, therefore, an object of the invention to simply provide a metal-based composite material having a good wettability between a porous structural body and a melt of a matrix metal and hence a good adhesion property therebetween in a low cost without conducting pressure application of preheating and adding specific component or compound having a high reactivity.
The inventors have made various examinations on the technique of effectively utilizing the active energy inherent to the free surface of the metal, particularly a technique of simplifying a composite formation course according to the molten metal penetrating method in order to solve the aforementioned problems in the composite formation of different metals. As a result, it has been confirmed that hydrogenatable metals (inclusive of alloys), for example, metals such as Ti, Ni, Fe, Co and the like or an alloy consisting essentially of these metals have a property of absorbing and releasing a gas of two atoms through a heating-cooling cycle (Sievert""s law: a solubility of a gas of two atom molecule such as hydrogen in a metal or the like at a certain temperature [% H] is proportional to a square root of partial pressure PH of the gas of two atom molecule at an equilibrium state).
Especially, it has been found that when such a characteristic of hydrogen that absorbability and releasability are excellent is given to these metals, the active state inherent to the free surface of the metal constituting the porous body is controlled, which can effectively be served to form the composite material.
Under the above situations, the inventors have made various studies for achieving the above object. As a result, it has been found out that a method wherein a porous body is shaped by using a hydrogenatable metal such as Ti Ni, Fe, Co or the like or an alloy consisting essentially of such a metal and a porous preform of a metal hydride is formed in at least a part of the resulting shaped body and a matrix metal of Al or Al alloy containing one or more selected from Mg, Cu and Si is impregnated into the preform through a molten metal penetrating method is effective as a method of forming a composite material. According to this method, when the metal hydride in the preform is heated to a temperature higher than the shaping temperature in the course of the composite formation, hydrogen is released to render the free surface of the metal constituting the porous body into an active state, whereby the good wettability to so-called molten matrix metal can be ensured.
That is, the invention is a technique of applying a phenomenon that certain kinds of metals or alloys have reversible property capable of absorbing or releasing hydrogen to the composite formation of metals, i.e. a technique of effectively utilizing the active energy inherent to the free surface of the metal for the composite formation.